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Appl Environ Microbiol, May 1998, p. 1750-1758, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Germination, Growth, and Sporulation of Bacillus thuringiensis subsp. israelensis in Excreted Food Vacuoles of the Protozoan Tetrahymena pyriformis

Robert Manasherob, Eitan Ben-Dov, Arieh Zaritsky, and Ze'ev Barak*

Department of Life Sciences, Ben-Gurion University of the Negev, Be'er-Sheva 84105, Israel

Received 30 October 1997/Accepted 12 February 1998

Spores of Bacillus thuringiensis subsp. israelensis and their toxic crystals are bioencapsulated in the protozoan Tetrahymena pyriformis, in which the toxin remains stable. Each T. pyriformis cell concentrates the spores and crystals in its food vacuoles, thus delivering them to mosquito larvae, which rapidly die. Vacuoles containing undigested material are later excreted from the cells. The fate of spores and toxin inside the food vacuoles was determined at various times after excretion by phase-contrast and electron microscopy as well as by viable-cell counting. Excreted food vacuoles gradually aggregated, and vegetative growth of B. thuringiensis subsp. israelensis was observed after 7 h as filaments that stemmed from the aggregates. The outgrown cells sporulated between 27 and 42 h. The spore multiplication values in this system are low compared to those obtained in carcasses of B. thuringiensis subsp. israelensis-killed larvae and pupae, but this bioencapsulation represents a new possible mode of B. thuringiensis subsp. israelensis recycling in nontarget organisms.

* Corresponding author. Mailing address: Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel. Phone: 972-7-6461-712. Fax: 972-7-6278-951. E-mail: Barakz{at}bgumail.bgu.ac.il.

Appl Environ Microbiol, May 1998, p. 1750-1758, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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